Apparatus for collection and removal of gases from an aluminum reduction cell

ABSTRACT

An apparatus for collecting and removing gases emitted by an aluminum reduction cell consists of at least one channel extending between a suction inlet and exhaust outlet. At least one curvilinear partition extends within the channel, so as to divide it into respective gas suction zones. Such zones are formed to change the direction of the gas flow from substantially vertical at the suction inlet to substantially horizontal at the exhaust outlet.

FIELD OF THE INVENTION

This invention relates to non-ferrous metallurgy in general, moreparticularly to gas collection and removal technology for production ofaluminum by electrolysis.

BACKGROUND OF THE INVENTION

Electrolytic cells are well known in the art of metallurgy andspecifically, in the production of aluminum by the electrolysis ofalumina. Such an electrolysis cell has a tank which is open at its upperend and whose base is formed by metal bars supporting blocks of carbon.The blocks of carbon are connected by a lining and act as a cathode. Thetank contains an electrolysis bath consisting of alumina dissolved incryolite which is heated to a temperature of about 950° C. to 1050° C.Anodes made of carbon are dipped into the cryolite bath.

When electric current is passed through the cell, the alumina decomposesinto aluminum and forms a metal bath which covers the cathode. Oxygengas is released during this process. As a result, the lower portion ofthe carbon paste anode cooks because it is dipped into the hightemperature electrolysis bath. Due to the presence of combustibleoxygen, the anode becomes burnt while the upper (undipped) portionsoftens. As the lower part is burnt by the oxygen, the carbon mass hasto be pushed downwards to keep the anode/cathode interval constant.

Combustion of the anode is accompanied by the substantial emission offumes consisting of gases such as carbon dioxide, carbon monoxide,sulfur dioxide, gaseous hydrofluoric acid, and particles of carbon,alumina, and fluorine-containing compounds. A solid crust typicallyforms on the top of the electrolytic cells. The crust traps gas in theelectrolytic cells forming a buildup of pressure. The crust may break inunpredictable places to alleviate the pressure buildup and allow thebuiltup gases to escape.

The gas contains noxious compounds which are detrimental to the healthof individuals and the environment. Therefore, the gas must be collectedand purified. The increased volume of production of electrolytic cellsis leading to an acute problem with regards to the gas collection andpurification. Due to the increased size and volume of productionfacilities as well as stringent regulations, costs of gas disposal areincreasing rapidly. Further, inefficient removal of gases from theelectrolytic cell compromises the efficiency of aluminum production andoften results in more gases being released into the workroom. Thus, theair of the building is more hazardous to breathe and extensive filtersand purification techniques are needed before the air is ventilated tothe atmosphere.

A typical method of collecting gases from the electrolytic cell involvescollecting the gases from the roof of a building or contained space. Thecollection unit will collect gas emitted from many individualelectrolytic cells. A large volume of air must be purified beforeexiting the facility, but the concentration of noxious fumes isgenerally low enough that it may be breathed, albeit uncomfortably. Topurify the amount of air in a large facility requires a vast andexpensive filtration system.

It is desired to filter the air closer to the source of the emission ofthe noxious fumes so that less air need be filtered and workers insidethe facility do not have to breathe the noxious fumes. U.S. Pat. No.4,668,352 and the USSR Patent Document 1473718 disclose means ofproviding suction and venting at regular intervals along theelectrolytic cell so as to provide predictable and efficient gasdiffusion. Each individual vent opens into a cross-section of theelectrolytic cell. The venting area of the cell is bisected byhorizontally placed walls spaced apart such that those walls higher inthe cell extend inward from the vent less distance than those lower inthe cell. Suction zones provided are approximately the width of twoflaps of the cell exhaust hood. The space between two neighboringpartitions is formed by two preset channels for gas removal from eachsuction zone, which converge into a common collector connected with thecentral suction device.

By this design, the inner bore of the electrolytic cell is divided bysolid wall-to-wall horizontal bafflers. The bafflers prevent placing ormoving an anode busbar or pins in this space. Channel geometry does notimpede deposition of alumina present in the flow of gases and therebycauses withdrawal thereof from the cell in significant quantity. Whilethis arrangement provides some improvement over the prior art gascollection systems, it causes formation of pockets of stagnation anddoes not contribute to the uniform gas collection and removal throughoutthe cell.

Further, Russian Federation Patent 2,218,453 discloses a system adaptedfor collection and removal of gases emitted from an aluminum reductioncell which comprises an anode beam formed with vertical walls, suctionwindows, and upper and lower stiffening members, so as to definechannels adapted for collection and removal of gases. The channels aredisposed in the top part of the anode beam, whereas each channel isprovided with inclined restrictive members forming a suction slit ofconstant width and variable height. The height of the channels increasein the direction of an end of the anode beam connected to the gasexhaust system.

From the detailed mathematical modeling based on a completethree-dimensional mathematical models of turbulent flows it is apparentthat these prior art arrangements do not provide uniform gas collectionalong the length of the cell. For example, in Russian Federation Patent2,218,453, gas collection is substantially more intensive at the outletbranch pipe of the central suction device than the rest of the system.More importantly, in one-sided gas collection, the gas collection systemappears to be practically inoperative at the portions thereof near theoutlet end. On the other hand, in the double-sided suction embodiment,three-dimensional models showed that suction was practicallynon-existent in the central section of the arrangement. The inclinedrestrictive members forming the suction slit of constant width andvariable height not only have actual effect on the uniformity of gascollection in the system, but actually provide highly undesirableadditional aerodynamic drag.

SUMMARY OF THE INVENTION

One aspect of the Invention provides an apparatus for collecting andremoving gases emitted by an aluminum reduction cell, and utilizing ananode beam formed with first and second walls spaced from each other soas to define a substantially hollow space therebetween. The apparatusconsists of at least one channel formed within the substantially hollowspace between said first and second walls, so as to extend between asuction inlet and an exhaust outlet. The suction inlet is associatedwith a gas collection system of the aluminum reduction cell. The channelis provided with at least one curvilinear partition extending betweenproximal and distal ends thereof and adapted to divide the channel intorespective gas suction zones, having gradually narrowing cross-sectionso as to change the direction of a gas flow in the suction zones fromsubstantially vertical at the suction inlet to substantially horizontalat the exhaust outlet.

According to another aspect of the invention, at least one partitionextends between a proximal end thereof situated at the suction inlet anda distal end thereof situated at the exhaust outlet. At least one gasflow regulating device is provided at the distal end of the partition,so as to regulate the gas flow within the respective suction zone. Thisgas flow regulating device includes a buffer flap which is movablyconnected to the distal end of the respective partition by a rotarydevice.

According to a further aspect of the invention, the first and secondwalls of the anode beam are substantially vertically oriented. At leastone channel is further defined by front and rear curvilinear walls. Atleast one partition is positioned between the front and rear walls. Thebuffer flap is movably connected to the distal end of the partition, soas to engage in one position the front curvilinear walls and in anotherposition to engage the rear curvilinear curvilinear wall of the channel.

As to still another aspect of the invention, the partition is formed bya concave bottom surface and by a convex top surface. These top andbottom surfaces meet each other at the proximal and distal ends thereof.In the channel the concave bottom surface of the partition faces thefront curvilinear wall and the convex top surface faces the rearcurvilinear wall of the channel.

As to still further aspect of the invention, upon changing the directionof the gas flow from substantially vertical to substantially horizontal,the gas flow goes through a 90° transformation within the respective gassuction zone. According to this aspect of the invention, multiplechannels are formed with the substantially hollow space. The at leastone curvilinear partition comprises multiple curvilinear partitionspositioned within the respective channels, so as to divide the channelsinto the respective multiple gas suction zones.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a longitudinal sectional view of one embodiment of the gascollection apparatus of the invention;

FIG. 2 is a cross-sectional view thereof;

FIG. 3 is a longitudinal sectional view of another embodiment of theapparatus of the invention; and

FIG. 4 is a chart illustrating the relationship between the verticalvelocity component of the gas flow with respect to the distance betweena particular location within the gas channel from the outlet branchpipe.

DETAILED DESCRIPTION OF THE INVENTION

Referring now to the drawings in general and to FIGS. 1 and 2 inspecific, a multidirectional embodiment of the gas collection andremoval device of the invention is depicted. More specifically, thesefigures illustrate a double-sided gas collection device having two gascollection branches 12 and 14, extending in opposite directions andoriginating from a common area. Each branch is adapted to collect andremove gases emitted from an aluminum reduction cell. These branchesform a part of an anode beam 1 of the respective cell having at least apair of spaced from each other substantially vertical walls 2 definingsubstantially hollow gas collection and removal channels 5. Top andbottom stiffness members 3 and 4 are provided to reinforce the channelstructure. Each channel extends between an inlet area 16 disposed in thevicinity of a suction window 9 and an outlet area 18 situated near anoutlet branch pipe 7. At least one curvilinear partition 6 is providedwithin the hollow area of each channel 5, so as to divide it into atleast two semi-independent sub-channels or suction zones 15. Eachcurvilinear partition 6 extends within the respective channel from theinlet area 16 to the outlet area 18. In the embodiment of the inventionillustrated in FIG. 1 the partitions 6 are formed by concave bottomsurface 17 and convex top surfaces 19 which meet at proximal edges 21and distal edges 23. The cross-section of each channel 5 graduallynarrows from the inlet to outlet and the direction of gas flow changesfrom the vertical to horizontal. In a similar manner, each suction zonegradually narrows and the direction of the respective gas flow changesfrom substantially vertical to substantially horizontal in anaerodynamic and efficient manner.

A gas flow regulating device 10 is provided at the distal end 23 of eachpartition 6 and is adapted to regulate the flow of the gases in theoutlet region of the respective suction zone and ultimately within theentire channel. In the preferred embodiment, as illustrated, for examplein FIG. 1, the gas flow regulating device 10 is in the form of a bufferflap 24 movably connected to a distal end 23 of the respective partition6 by the rotary arrangement 26. The length of the flap 24 is enough topartially or fully close the corresponding sub-channel or suction zone15 upon activation of the rotary arrangement 26.

Each channel is further defined by front 25 and rear 27 curvilinearwalls. The shape of each sub-channel 15 is enhanced by the fact that inone instance the concave bottom surface 17 of the partition faces theconvex rear wall 27 and in the other instance the convex top surface 19of the partition faces the front concave wall 25 of the channel. Thepartition 6 is positioned between the front and rear walls, whereas thebuffer flap 24 is movably positioned at the respective distal end 23 ofthe partition. Thus, in one mode the buffer flap 24 either moves in thedirection of or engages the front curvilinear wall 25 and in anothermode it is adapted for movement toward or engagement with the rearcurvilinear wall 27.

In order to maintain the required rate of flow, in each channel 5 gasesfrom the sub-channels or individual suction zones 15 are collected bythe gradually narrowing outlet region 18 associated with the outletbranch pipe 7. As the gases rise from the suction windows 9 and inletarea 16 towards the outlet area 18, the rate of gas flow is kept atequilibrium within each suction zone 15 by gradually decreasingcross-sectional area thereof. Further, the configuration of curvilinearwalls of the channels and the respective surfaces of partitions enablesthe invention to smoothly change the gas flow from a substantiallyvertical direction to a substantially horizontal direction. Morespecifically, as illustrated in FIG. 1, in each channel 5 and suctionzone 15 the direction of the gas flow goes through about a 90°transformation, i.e. from substantially vertical at the inlet 16 tosubstantially horizontal at the outlet area 18, before it is fed via anoutlet branch pipe 7 into a common collector (not shown) and further tothe reduction plant gas collection system.

The combination of smooth curvilinear walls of the channels withaerodynamically sophisticated design of the partitions 6 minimizesformation of undesirable turbulences, assures a laminar gas flow, andprevents alumina deposition on the walls of gas collection system. Inthe arrangement of the invention, the channels 5 and the sub-channels orsuction zones 15 have no “dead” regions or locations where gas stagnatesand crust or residue builds up. As well known from the prior art, suchresidue impedes flow, changes the dynamic flow of gas, and reducesefficiency of the entire gas evacuation system. In the aluminumproduction plant, eventually the gas collection and removal system mustbe stopped, cleaned, and reset. The present arrangement allows for theprocess of reduction of aluminum to continue unabated for longer periodsof time, thus, increasing efficiency of an entire plant.

Referring now to FIG. 3 of the drawings, wherein a unidirectionalembodiment of the gas collection and removal apparatus of the inventionis illustrated. This figure depicts a single-sided gas collection devicehaving one gas collection branch provided to collect and remove gasesemitted from aluminum reduction cells. Similar to the previouslydiscussed arrangement, this embodiment also forms a part of the anodebeam 1 defined by at least a pair of spaced from each othersubstantially vertical walls 2 forming the substantially hollow gascollection and removal channel 5. Top and bottom stiffness members 3 and4 are also provided to reinforce the structure. The channel 5 extendsbetween the inlet area 36 formed with multiple suction windows 9 and acommon outlet area 38 situated in the vicinity of the branch pipe outlet7. In the channel the direction of gas flow changes from vertical tohorizontal and the cross-section thereof gradually narrows from theinlet to outlet.

Multiple curvilinear partitions 6A, 6B, and 6C are provided within thechannel 5, so as to form multiple semi-independent sub-channels orsuction zones 35A, 35B and 35C. Each curvilinear partition extends fromthe inlet area 36 toward the outlet area 38. The partitions 6A, 6B, and6C are formed with somewhat similar concave-shaped bottom surfaces 37A,37B, and 37C, respectively. However, the shape of the top surface variesfrom one partition to another. In this respect, the first partition 6A,according to the gas flow direction, is formed with the top surface 39Ahaving a semi-convex configuration with an elongated portion 40Aextending toward the distal edge thereof. The top and bottom surfacesmeet at proximal and distal edges, so as to define a body having asophisticated aerodynamic configuration. A hollow interior of the bodyof the partition is adapted to accommodate ducts 8 which can be used forthe installation of anode busbar struts. A cross-sectional configurationof the second partition 6B is somewhat similar to that of the firstpartition 6A and is formed with an angle-shaped proximal end area. Anelongated, substantially flat portion 40B is provided at the distal areathereof or at the intersection between the top 39B and bottom 37Bsurfaces of the second partition. The elongated portion 40B is orientedwithin the channel 5 along the direction of movement of the gases andhas a substantial length reaching the outlet area 38. The thirdpartition 6C is defined by the top and bottom surfaces 39C and 37C,respectively, so as to form an aerodynamically shaped body having ahollow interior. The elongated portion 40C is oriented in asubstantially parallel manner to the elongated portion 40B of the secondpartition. As illustrated in FIG. 3, the outlet portion of the suctionzone 35C formed between the second and third partition extends into thecontinuous area between elongated portions 40B and 40C. The sectionzones 35A and 35B merge at the outlet area 38, so that the commonportion thereof is arranged in a substantially parallel manner to theoutlet portion of the suction zone 35C.

Similar to the configuration of the respective channel, cross-sectionsof each sub-channel or suction zone gradually narrows and the directionof the respective gas flow changes from substantially vertical tosubstantially horizontal in an aerodynamic and efficient manner.

In a previously discussed manner, the gas flow regulating devices 10 areprovided at the distal end of each partition, so as to regulate the flowof the gases in the respective sub-channels or suction zones 35A, 35B,and 35C and ultimately within the entire channel 5. The gas flowregulating devices 10 are in the form of buffer flaps which are movablyconnected to the distal ends of the respective partitions by the rotaryarrangements. The length of the flaps is substantial enough to regulatemovement of gases by partially or fully closing the correspondingsuction zones. In view of the substantial length of the elongatedportions 40B and 40C, the outlet area of the suction zones 35B and 35Chave a substantially uniform cross section and are terminated in theclose vicinity of the outlet branch pipe 7.

In the embodiment of FIG. 3, the channel 5 is further defined by thefront 25 and rear 27 curvilinear walls. As the gases rise within therespective suction zones from the inner area toward the outlet area, theflow direction is converted from a substantially vertical to asubstantially horizontal configuration.

In the apparatus of the invention the cross-section of each sub-channelor suction zone 15, 35 and the respective channels 5 are adjustedaccording to a predetermined pattern. The cross-sectional area of theoutlet region 18, 38 of the channel is substantially decreased by thevirtue of its design in comparison to the rest of the channel. In thismanner, the gas flow is accelerated to a higher velocity upon exitingthe outlet region. Furthermore, by utilizing the flow controllingarrangement 10 having movable buffer flaps, the gas flow within therespective channels can be further limited to a particular sub-channelor suction zone or a restricted area thereof. As the cross-sectionalarea of the sub-channel is restricted, the velocity of the gas flowpassing therethrough is accelerated even further. Thus, the device ofthe invention provides a positive impulse for the gas flow, upon itsentering into the main duct of the gas evacuation system. In view of theabove, the typical amount of energy loss and pressure drop in the mainduct is considerably reduced. This is because the energy requirement forthe entire gas transportation system has been reduced.

In the plant evacuation system, gases are conveyed out of the suctionzones and into the output duct. In the device of the inventionadditional energy is acquired in the sub-channels or suction zones 15 toallow the gas to enter into the output duct at a greater velocity. Thus,the present invention provides a gas transportation system with aconsiderable reduction of the energy consumption.

Aluminum reduction provides a level of unpredictability of gasproduction. Unknown variables include the precise amount, temperatureand so forth of the gas itself. Further, external factors such asambient temperature and precise heat capacity of the electrolytic cellalso affect the system. To compensate for these and other factors, asdescribed hereinabove, the gas flow regulating devices 10 can be used topartially or fully close a specific sub-channel or suction zone 15.Doing so allows the gas flow to be diverted to the adjacent sub-channel.Unforeseen or unpredictable gas flow variations can be compensated forby directing the gas flow through various sub-channels to maintainequilibrium. A versatility of the gas evacuation system is increased bypartially or fully closing a specific sub-channel or suction zone, so asto increase pressure in that part of the system and decrease flow.

In the apparatus of the invention gas volume is regulated within theindividual sub-channels by the gas flow regulating devices which includebuffer flaps movably connected to the distal ends of the curvilinearpartitions. The inner spaces of the sub-channels and channels remainfree and unobstructed for installation of the automatic feedings systemwhich provides daily alumina stock. Another positive aspect of theapparatus of the invention is that a part of the wall structure remainsfree for the formation of the windows passing through such walls andprovided for installation of anode bar struts.

Referring now to FIG. 4, a chart illustrating the relationship betweenthe vertical velocity component of the gas flow and the distance betweena particular location within the channel from the outlet branch pipe isdepicted. The chart illustrates the uniformity of the gas flow withinthe device of the invention which is based on the results of thedetailed mathematical modeling which are in turn based on complete3-dimensional models of the turbulent flows. The curve 1 of this figurereflects the average vertical velocity at the inlet area of the device.The curve 2 reflects the average vertical velocity in the prior artdevices. It is clear from the chart of FIG. 4 that as the distance of aparticular location within the channel from the outlet branch pipeincreases the gas flow on the device of the present inventioncorresponds substantially lower vertical velocity component compared tothe prior art devices.

1. An apparatus for collecting and removing gases emitted by an aluminumreduction cell, said apparatus utilizing an anode beam of said sellformed with first and second walls spaced from each other so as todefine a substantially hollow space therebetween, said apparatuscomprising: at least one channel formed within said substantially hollowspace between said first and second walls, said at least one channelextending between a suction inlet and an exhaust outlet, said suctioninlet being associated with a gas collection system of said aluminumreduction cell, said at least one channel is provided with at least onecurvilinear partition extending between proximal and distal ends thereofand adapted to divide said channel into respective gas suction zones,having gradually narrowing cross-section so as to change the directionof a gas flow in said suction zones from substantially vertical at saidsuction inlet to substantially horizontal at said exhaust outlet.
 2. Theapparatus according to claim 1, wherein said at least one partitionextends between a proximal end thereof situated at the suction inlet anda distal end thereof situated at the exhaust outlet, at least one gasflow regulating device is provided at said distal end of the partition,so as to regulate the gas flow within the respective suction zone. 3.The apparatus according to claim 2, wherein said at least one gas flowregulating device comprises a buffer flap movably positioned at saiddistal end of said at least one partition.
 4. The apparatus according toclaim 3, wherein said buffer flap is movably connected to said distalend of said at least one partition by a rotary device.
 5. The apparatusaccording to claim 4, wherein said first and second walls of the anodebeam are substantially vertically oriented, said at least one channel isfurther defined by a front and rear curvilinear walls, said at least onepartition being positioned between said front and rear walls, saidbuffer flap is movably positioned at said distal end of the partition,so as to engage in one position the front curvilinear walls and inanother position to engage the rear curvilinear curvilinear wall of saidchannel.
 6. The apparatus according to claim 5, wherein said at leastone partition is formed by a concave bottom surface and by a convex topsurface, said top and bottom surfaces meet each other at said proximaland distal ends of the partition.
 7. The apparatus according to claim 6,wherein in said at least one channel said concave bottom surface of thepartition faces the front curvilinear wall and said convex top surfacefaces the rear curvilinear wall of the channel.
 8. The apparatusaccording to claim 1, wherein upon changing the direction of gas flowfrom substantially vertical to substantially horizontal, said gas flowgoes through a 90° transformation within the respective gas suctionzone.
 9. The apparatus according to claim 2, wherein said at least onepartition is formed having substantially hollow interior.
 10. Theapparatus according to claim 1, wherein at least one channel comprisesmultiple channels formed with the said substantially hollow space, saidat least one curvilinear partition comprises multiple curvilinearpartitions positioned within said respective channels, so as to dividesaid channels into the respective multiple gas suction zones.